GPU computation difference between rendering and cloth baking
Besides the OpenGL viewport preview, GPU Acceleration inside Blender can only be used currently for rendering with the Cycles Render Engine using either CUDA on NVidia GPUs or OpenCL for AMD Graphics cards on certain supported hardware. OpenCL acceleration may also be used on the compositor for image processing.

Physics baking, particles and cloth simulation and all other areas currently only use CPU, as far as I know.